There is substantial literature in the art with respect to the hydrogenation of aromatic amines, including bridged aromatic amines, e.g., methylenedianiline to produce 4,4'-methylenedi(cyclohexylamine), also called bis(para-aminocyclohexyl)methane, bis (4-aminocyclohexyl)methane and PACM.
Some of the early hydrogenation work to produce aromatic amines, such as, PACM, was done by Whitman and Barkdoll, et al. and their work is set forth in a series of U.S. Pat. Nos., e.g., 2,511,028; 2,606,924; 2,606,925; and 2,606,928. Basically the processes described in these patents involve the hydrogenation of methylenedianiline at pressures in excess of 200 psig, preferably in excess of 1,000 psig, at temperatures within a range of 80.degree. to 275.degree. C. utilizing a ruthenium catalyst. The hydrogenation is carried out under liquid phase conditions and an inert organic solvent is used in the hydrogenation process. Typically, a liquid product having a trans, trans- isomer content of 15-23% is obtained. Examples of ruthenium catalysts utilized for the hydrogenation process include ruthenium oxides such as ruthenium sesquioxide and ruthenium dioxide; and ruthenium salts.
Brake, et al. in U.S. Pat. Nos. 3,696,108 and 3,644,522 continued in the development of processes for manufacturing PACM by hydrogenating methylenedianiline. They found that if the ruthenium was carried upon a support and the support was alkali-moderated, the catalyst was much more active and catalytically effective in producing the desired hydrogenated PACM product. Alkali moderation was effected by contacting the catalyst and support with alkali metal hydroxide or an alkoxide; also, such alkali moderation of the catalyst could be effected prior to hydrogenation or in situ during the hydrogenation.
U.S. Pat. Nos. 3,347,917; 3,711,550; 3,679,746; 3,155,724; 3,766,272 and British Patent 1,122,609 disclose various isomerization processes and hydrogenation processes to produce PACM containing high trans,trans- isomer content; i.e. an isomer content near equilibrium typically 50% trans,trans-, 43% cis,trans- and 7% cis,cis-. As in the early work ruthenium catalysts usually were used to effect isomerization. High temperatures and longer reaction times were required to produce the high trans,trans- product and, in addition, considerable deamination of product took place.
A wide variety of catalytic systems have been developed for the hydrogenation of aromatic amines, and typical catalytic systems are represented in the following patents:
U.S. Pat. No. 3,591,635 discloses the use of rhodium on alumina as a catalyst for the hydrogenation of methylenedianiline.
U.S. Pat. No. ,946,998 discloses processes for the hydrogenation of methylenedianiline contaminated with impurities utilizing a mixture of rhodium and ruthenium on alumina as the catalyst. A hydrogenated methylenedianiline product having a trans, trans- isomer content of from about 14 to 28% is prepared using the mixed metal catalyst system, although higher trans, trans- isomer content can be achieved through high temperature, long reaction times, and high ruthenium concentration. The presence of rhodium permits lower operating temperatures and reduces the percent trans, trans- isomer.
U.S. Pat. No. 4,960,941, similar to U.S. Pat. No. 4,946,998 and disclose the hydrogenation of crude methylenedianiline containing up to about 15% oligomers using a mixed metal catalyst system. The catalyst comprises rhodium and ruthenium, the '941 patent showing a preference for the rhodium being carried on a titania support.